Mold for injection molding of a flexible tube and injection molding method

ABSTRACT

The invention concerns in particular a mould for injection moulding of a flexible tube, said mould comprising as moulding tools, a nozzle receptacle ( 1 ), an impression ( 2 ) and a core ( 3 ), housed in a stack of plates (P 4 , P 5 , P 6 , P 7 ). The invention is characterised in that said moulding tools ( 1, 2, 3 ) have pairs respective conical support surfaces ( 101, 201, 301, 102. 302 ), through which the tools are centred and aligned with one another, each support surface being formed by a portion of tools deprived of transverse mobility.

[0001] The present invention concerns, in general, the techniques forinjection molding of hollow bodies such as those made of thermoplasticmaterials.

[0002] More specifically, the invention concerns, according to one ofits features, a mold for the injection molding of a tube presenting adistribution spout supporting a neck which tapers radially to a tubularskirt and made of a thermoplastic injection material which is flexibleat room temperature, said mold comprising plates which are applied oneon the other to form a stack that follows an injection direction that istransverse with respect to the plates, from a first side where a hotblock is located, which contains the molten injection material, to asecond side which is at a distance from the first side, and a set ofmolding tools comprising at least one nozzle receptacle, an impression,and a core housed in the stack of plates, the nozzle receptacle beingadjacent to the hot block and accommodating a nozzle, which has an inletthat communicates with the hot block and an outlet that communicates,with a molding cavity through an injection passage, the core comprisingat least a first base that is elongated, following a direction that isthe reverse of the injection direction, by a molding pin housed in theimpression and ending in a free end, the molding cavity being delimitedby at least the nozzle receptacle, the impression, and the molding pinof the core and extending in the injection direction from the injectionpassage, the core being held in the stack of plates by at least its baseand by the free end of the molding pin, and the stack of platescomprising two blocks, which are selectively applied against each otherat an interface between two adjacent plates forming a mold joint thatallows, as desired, the opening or closing of the mold.

[0003] Molds of this type are used today to injection-mold cartridgesrigid at room temperature, closed by a piston, and intended to containviscous materials such as glues or mastics.

[0004] These molds are not suited for the preparation of tubes that areflexible at room temperature and that are resistant to cracking understress, such as tubes used for the packaging of cosmetic products.

[0005] Indeed, the manufacture of these tubes implies the use of highlyviscous materials to impart the required flexibility in order to ensurethe resistance of the thin walls to cracking under stress.

[0006] These highly viscous materials, which are shaped to form a thinwall must be injected at high pressure. Thus, the mold must be designedto resist deformations that may occur during injection due to the effectof the thrust of the material in the mold.

[0007] Moreover, these tubes must have a resistance to cracking understress that is equal at all points of their walls. Therefore, it isnecessary for the wall thickness to be perfectly uniform and for thedifferent sheets of injected molten material that form the tube torejoin as quickly as possible and to become welded to each other in anoptimal manner.

[0008] More generally, the invention concerns the architecture and themolding functions of injection, cooling, and ejection for injectionforming a flexible tube, given the specific stresses inherent in thematerial used and its flexibility, dimensions, and the shape of theflexible tube.

[0009] The purpose of the invention is to propose a mold which iscapable, even in its most elementary embodiment, to solve at least oneof these problems.

[0010] For this purpose, the mold of the invention, which also is inconformity with the generic definition given in the preamble, isessentially characterized in that the set of molding tools comprising atleast the nozzle receptacle, the impression, and the core, presentrespective pairs of at least partially conical support surfaces whichare aligned in the direction of injection, in that these molding toolsare mutually centered and aligned with one another, by pairs of toolsbeing constituted next to each other, by means of an axial force thatmoves the respective support surfaces of the tools of each constitutedpair together, and in that each support surface of each tool of eachconstituted pair is formed by a part of this tool that is deprived offunctional mobility in the direction traverse to the injectiondirection.

[0011] The support surface can thus form, as a result of two-by-twocontact, at least three interfaces through which the molding tools areapplied, two-by-two, and with centered support one against the other,where the support surfaces presented by the molding tools for each ofthese three interfaces preferably consist of respective single-blockparts of these molding tools.

[0012] The nozzle receptacle and the impression can each even beintegrally formed from a single piece.

[0013] In the preferred embodiment variant of the invention, the moldjoint passes between the nozzle receptacle and the impression.

[0014] To further improve removal from the mold, the molding pinadvantageously presents a surface state which, in order to produceminimal adhesion of the tube to this molding pin after injection, is atleast equivalent to the surface state obtained by the application of atleast one of the surface treatments consisting of sandblasting,micro-finishing, a laser treatment, and a chemical treatment.

[0015] To improve the homogeneity of the injected tube, the pair ofsupport surfaces which the core and the nozzle receptacle presentpreferably consists of a concave support surface of the core and aconvex support surface of the nozzle receptacle, which results in thedistribution spout of the tube terminating in a cup.

[0016] In the mold of the invention, the nozzle receptacle can be formedto mold at least one external surface of the neck of the tube up to azone of connection with the skirt.

[0017] The molding pin of the core itself may extend from the first baseand mold an internal surface of the skirt; it may present a shoulderwhich borders its free end and which is capable of molding an internalsurface of the neck.

[0018] Moreover, the core preferably comprises an external part and aninternal part, which are shaped so that the internal part extends, alonga direction which is the reverse of the injection direction, from asecond base of the core to a tip which is arranged at the free end ofthe molding pin, and so that the internal part is mounted axially sothat it can slide in the interior of the external part between a supportposition, for which the tip is supported on the nozzle receptacle, andan open position, for which the tip is distant from the nozzlereceptacle.

[0019] Under these conditions, the tip of the internal part of the corecan mold an internal surface of the spout, and the slides can be mountedso they can be moved in translational movement in radial recesses of thenozzle receptacle to mold an external surface of the spout, where theseslides can close, in a sealing manner, in the open position and in theclosed position, the recesses of the nozzle receptacle in which they aremounted so they can move.

[0020] In particular, the slides can be two in number, they can bearranged so they are aligned with one another on both sides of theinjection passage, and they can be mounted so they can move,transversely with respect to the injection direction, between a closedposition where they are in contact and an open position where they aremutually separated form each other, the nozzle receptacle beingpenetrated by an air conduit which opens between the slides and isconnected to a pressurized air source, and the slides close and open theair conduit in their closed position and in their open position,respectively.

[0021] In the case where the core is made up of two parts, the mold cancomprise on the second side, a hydraulic cylinder which selectivelydisplaces the second base of the core, where this hydraulic cylinder, toobtain the centering support of the core on the nozzle receptacle, candisplace the second base of the core, along a direction which isopposite the injection direction, to a stop which defines a length ofthe internal part of the core for which this internal part of the coreundergoes elastic compression due to the support of its point on thenozzle receptacle.

[0022] The hydraulic cylinder is preferably a double-acting hydrauliccylinder capable of selectively releasing the second base of the corealong the direction of injection after the injection of the skirt of thetube, thus making it possible to separate the tip and the nozzlereceptacle from each other.

[0023] To obtain an adequate cooling of the mold, the internal part ofthe core is advantageously traversed by an axial channel in which ishoused a hollow needle which extends from a connection end which isarranged in the second base of the core to a distribution end, arrangedin proximity of the tip of this internal part, where the connection endof this needle, dependent on the mold, is connected to a source ofcooling fluid, and the needle and the axial channel are separated fromeach other by an interstice which presents to the fluid injected in theneedle a circulation path which returns to the second base of the core.

[0024] In addition, it can be useful to use an arrangement such that theinternal part and the external part of the core both present first axialsections and second axial sections, where the second ones are relativelycloser to the tip than the first ones, and the first axial sectionsachieve, between the internal part and the external part of the core, athermal coupling which determines a first thermal flow, such that thesecond axial section achieves, between the internal part and theexternal part of the core, a thermal coupling determining a secondthermal flow and such that the second flow is greater than the firstflow.

[0025] If the molding tools are arranged, one with respect to another,with a maximum clearance, and if they are arranged, with respect to theplates, with a second maximum clearance, one should proceed in such amanner that the second maximum clearance is greater than the firstmaximum clearance, and so that the plates are regulated as far as theirtemperature is concerned to present a differential dilatation betweenthemselves, which is less than the second maximum clearance.

[0026] The injection passage preferably comprises a central feed channeland radial feed channels, each one of which extends from the centralchannel to a zone of connection to the spout, where this radical channelpresents a connection width and where the spout presents a predeterminedperimeter, and the added widths of the radial feed channelsadvantageously present at least 15% of the predetermined perimeter ofthe spout, or, even more advantageously, more than 25% of thepredetermined perimeter of the spout.

[0027] In this case, the radial channels can, in addition, present awidth which increases, along a centrifugal radial direction, until itreaches a maximum width in the zone of connection to the spout.

[0028] To improve the spread, in the form of a sheet, of the injectedmaterial, the molding cavity preferably presents an annular narrowedzone beyond the zone of connection of each radial channel to the spout.

[0029] To guarantee a fixed radial position for each slide in the closedposition of the mold, this slide is preferably connected, at a distancefrom the injection passage, to an inclined surface of the first block ofplates, which works in cooperation with an inclined surface of thesecond block of plates.

[0030] To prevent any residual adhesion of the injection material to thenozzle, the latter can comprise, between its inlet and its outlet, astop plug which makes it possible to interrupt a flow of injectionmaterial from the hot block toward the injection passage, at the outletof the nozzle.

[0031] The mold of the invention can be shaped so that the internalsurface and the external surface of the skirt form, between them, in amid-plane of the tube, an angle of less than 0.002 radians, the skirtthus presenting over its entire surface a very homogenous resistance todeformation.

[0032] The invention also concerns a method for the manufacture of atube presenting a distribution spout on top of a neck which tapersradially to a flexible tubular skirt, where this method essentiallycomprises a molding phase and a mold removal phase, the molding phaseconsisting in forming the tube by injecting, through an injectionpassage, a molten thermoplastic injection material into a molding cavitypresenting a mold joint and at least partially delimited by a core andan impression, the spout being molded in a part of the molding cavitywhich is adjacent to the injection passage; and the mold removal phase,which follows the molding phase after solidification of the injectedmaterial, and comprising a holding operation which consists intemporarily holding the tube, a mold release operation which consists inpartially extracting the core from the tube, an opening operation whichconsists in opening the molding cavity, and an ejection operation whichconsists in ejecting the tube from the molding cavity, where the openingoperation follows to the mold release operation, and consists in openingthe molding cavity at the mold joint, between the neck and the skirt ofthe nozzle.

[0033] According to the invention, this method is essentiallycharacterized in that it comprises an accompanying operation,concomitant with at least one of the operations of mold release and ofrelease, and consisting in blowing in air between the core and the tube.

[0034] Moreover, the holding operation is preferably carried out byholding the tube by the spout by means of slides which have been placedbeforehand in a mutually close position before the molding operation,where this holding operation is continued during the opening operation.

[0035] The ejection operation can essentially consist of interruptingthe holding operation by separating the slides from each other and byblowing air between the separated slides and an external surface of thespout.

[0036] Finally, the holding operation is preferably interrupted beforethe end of the opening operation, so that the tube formed falls by itsown weight between the two parts of the open mold.

[0037] Other characteristics and advantages of the invention will becomeclear from the description below, which is given for the sake ofinformation and without limiting the scope of the invention, withreference to the drawings in the appendix, wherein:

[0038]FIG. 1 is a cross-sectional view of a mold according to theinvention, where the section is taken along a first plane that includesthe direction of injection;

[0039]FIG. 2 is a cross-sectional view of a detail of the mold of FIG.1, represented in larger scale, the section being taken along a secondplane that includes the direction of injection and is perpendicular tothe plane of FIG. 1;

[0040]FIG. 3 is a cross-sectional view of an enlarged detail of the moldof FIG. 2 and of the tube represented at the end of the injectionprocess;

[0041]FIG. 4 is an enlarged cross-sectional view of the nozzlereceptacle shown in FIG. 1;

[0042]FIG. 5 is a top view of the nozzle receptacle shown in FIG. 4;

[0043]FIG. 6 is an enlarged cross section of the nozzle receptacle asrepresented in FIG. 2;

[0044]FIG. 7 is a partial enlarged cross-sectional view of the nozzlereceptacle as shown in FIG. 6;

[0045]FIG. 8 is a top view of the interface of mutual support of the tipof the core and of the nozzle receptacle;

[0046]FIG. 9 is an enlarged partial cross-sectional view of the spout ofthe tube after injection;

[0047]FIG. 10 is a schematic cross-sectional view of the part of themold in the vicinity of the spout of the tube.

[0048] For convenience and in conformity with the figures, the mold isviewed with an orientation in which the spout of the tube is locatedabove the skirt of the tube, where it is understood that in practice theuse of the mold tends to be such that the injection direction of thetube is horizontal.

[0049] The invention concerns a mold which allows the injection of atube T which is partially shown in FIG. 3 and which is made of athermoplastic injection material which is flexible at room temperature.

[0050] This tube presents a distribution spout D which is above the topof neck C, the latter tapering radially to a tubular skirt J.

[0051] As shown in FIG. 1, the mold first comprises a set of platesP1-P8 which are applied one to another, and which form a stackconsisting of two blocks E10 and E20.

[0052] This stack extends, along a direction of injection, noted X1 andtransverse with respect to the plates P1-P8, from the first side E1 to asecond side E2, which is at a distance from the first side E1.

[0053] The blocks E10 and E20 are intentionally applied against eachother at the interface, which is also the interface between the twoadjacent plates P3 and P4, and which forms a mold joint PJ that allowsthe opening and the closing of the mold. On the first side E1 of themold, a hot block Q is provided, which is a reservoir intended tocontain the molten injection material.

[0054] Moreover, the mold comprises a set of molding tools, comprising anozzle receptacle 1, an impression 2 and a core 3, and which are housedin the stack of plates.

[0055] The nozzle receptacle 1, which is shown in detail in FIGS. 4-7,is adjacent to the hot block Q and it is intended to receive a nozzle 4,which is only visible in FIGS. 1 and 10.

[0056] An inlet 41 of the nozzle 4 communicates with the hot block Q,and an outlet 42 of said nozzle (FIG. 10) communicates, via an injectionpassage 14, with a molding cavity K (FIG. 2) into which the materialintended to constitute the tube is injected.

[0057] The core 3 comprises a first base 31 which is extended, along adirection X 2 which is the reverse of the injection direction X1, by amolding pin 36 housed in the impression 2 and ending by a free end 361(FIG. 3).

[0058] Under these conditions, the molding cavity K is delimited by thenozzle receptacle 1, by the impression 2, and by the molding pin 36 ofthe core 3; and it extends, along the injection direction X1, from theinjection passage 14.

[0059] As shown first in FIG. 2, the core 3 is maintained in the stackof plates by its base 31, and by the free end 361 of the molding pin 36.

[0060] According to a specific feature of the invention, the moldingtubes formed by the nozzle receptacle 1, the impression 2, and the core3, present pairs of respective support surfaces, referenced 101 and 102,for receiving the nozzle, 201 and 202 for the impression, 301 and 302for the core 3, these pairs of support surfaces being at least partiallyconical and oriented along the injection direction X1.

[0061] According to a second specific feature of the invention, thesemolding tools, 1, 2 and 3 are mutually centered and aligned with respectto one another, by the pairs of tools which are constituted next to eachother and which are represented by the pairs 1-2, 2-3 and 3-1, by meansof an axial force F1+F2 (FIGS. 1 and 2) which moves the respectivesupport surfaces of the tools of each constituted pair 1-2, 2-3 and 3-1toward each other, that is, the support surfaces 101 and 201 for thenozzle receptacle and the impression, the support surfaces 202 and 301for the impression and the core, and the support surfaces 302 and 102for the core and nozzle receptacle.

[0062] Finally, according to a third specific feature of the invention,each support surface of each tool of each of the constituted pairs 1-2,2-3 and 3-1, that is, each of the support surfaces 101, 201, 202, 301,302 and 102 is formed by a part of the corresponding tool which hisdeprived of functional mobility in the direction traverse with respectto the injection direction X1, where this part is thus fixed or movablealong only one direction that is essentially parallel to the injectiondirection X1.

[0063] In the illustrated embodiment variant, the axial force F1+F2consists of a force of F1 (FIG. 1), which moves the plates against eachother, and a force F2 (FIG. 2), which moves the core 3 against thenozzle receptacle 1; this will be described in greater detail below.

[0064] Thus, the support surfaces 101, 102, 201, 202, 301 and 302 form,via two-by-two contact, three interfaces, designated 101-201, 202-301,and 302-102, and by which the molding tools 1, 2 and 3 are appliedtwo-by-two with centering support against each other.

[0065] Moreover, to ensure a precise positioning of the molding toolsone with respect to another, the support surfaces 101, 102, 201, 202,301 and 302 presented by these molding tools to each one of these threeinterfaces 101-201, 202-301, 302-102 are formed by respectivesingle-block parts of these molding tools 1, 2, 3.

[0066] In other words, the molding tools are each formed from a singlepiece, at least at the location of their support surface, where thenozzle receptacle 1 and the impression 2 can themselves each beintegrally formed from a single piece.

[0067] In the preferred and illustrated embodiment variant of theinvention, the mold joint PJ passes between the nozzle receptacle 1 andthe impression 2; that is, the plates P3 and P4 can be easily separatedfrom each other.

[0068] To facilitate the removal of tube T from the mold, the moldingpin 36 is preferably subjected to at least one surface treatment chosenfrom the group of surface treatments consisting of sandblasting,micro-finishing, a laser treatment, and a chemical treatment, and whoserole is to reduce the surface roughness of the molding pin.

[0069] For example, the latter can be subjected to sandblasting,followed by a micro-finishing, optionally followed by a laser treatmentwhich effects superficial melting of the surface.

[0070] In the case where sandblasting is carried out, it can be veryadvantageously followed by a treatment capable of eliminating theresulting micro-points, for example by micro-finishing.

[0071] Similarly, in the case where micro-finishing is carried out, thetreatment is very advantageously preceded by a treatment which causesmicroroughness in the treated surface, for example by sandblasting.

[0072] Other surface treatments can optionally be chosen provided thatthey do not lead, in comparison to the treatments cited above, to ahigher adhesion of the tube T to the molding pin 36 after injection.

[0073] The pair of support surfaces 302 and 102 which the core 3 and thenozzle receptacle 1 present, moreover, preferably consists of a concavesupport surface 302 of the core 3 and a convex support surface 102 ofthe nozzle receptacle 1.

[0074] Due to this characteristic and the initial kinetic energy of thematerial which is injected through the passage 14, the central feedchannel 40, and the radial channels 44-46, which will be betterdescribed below, the material is laterally deflected along an annulardirection with respect to the contact zones Z of the radical channelsand of the spout D, during the injection.

[0075] This spreading itself has the effect that the different sheets ofmolten injection material which move into the molding cavity K, startingfrom different radial channels 44-46, rejoin and become fused to eachother, and thus the spreading of the injection material is ashomogeneous as possible.

[0076] Correlatively, as shown in FIG. 3, the distribution spout D ofthe injected tube ends in a cup, which imparts to the finished tube,after perforation of the cup, a particular user comfort, associated withthe matching of the finger to the cup and also with the fact that anyexcess product that exits the tube is temporarily contained in the cupand can be returned to the tube due to the suction effect produced bythe latter as soon as the pressure which deformed it is released.

[0077] As shown in FIG. 3, the nozzle receptacle 1 is shaped to mold theexternal surface Ce of the neck C of the tube, to the zone of connectionZc of the neck C to the skirt J, while the molding pin 36 of the core 3,which extends from the first base 31 (FIG. 2), molds the internalsurface Ji of the skirt J and presents a shoulder 362 which borders itsfree end and which makes it possible to mold the internal surface Ci ofthe neck C.

[0078] In the preferred embodiment variant of the invention, at thelevel of the molding pin 36, the core 3 in fact comprises an externalpart 33 and an internal part 34.

[0079] The internal part 34 of the core 3 extends, along the directionX2, which is the reverse of the injection direction X1, from a secondbase 32 of the core 3 to a tip 343, which is arranged at the free end361 of the molding pin 36.

[0080] The internal part 34 of the core 3 is mounted so that it canaxially slide in the interior of the external part 33 between a supportposition, illustrated in the left half of FIG. 2, and in which the tip343 rests against the nozzle receptacle 1, and an open position,illustrated in FIG. 3 on the right half of FIG. 2, and in which the tip343 is at a distance for the nozzle receptacle 1.

[0081] More specifically, the internal part 34 of the core, of which thetip 343 molds an internal surface Di of the spout D, is located in itssupport position for the entire time during which the skirt J andoptionally the neck C are injected, and it does not adopt its openposition except for the injection of the spout D, or at least of the cupwhich closes it (FIG. 3).

[0082] The external surface De of the spout D is molded by slides 11, 12(FIG. 1, 3 and 10) which are mounted so that they can undergotranslational movement, transverse to the injection direction X1, in theradial recesses 110, 120 of the nozzle receptacle 1, and which close thelatter in a sealing manner.

[0083] The slides 11, 12, which are preferably two in number, arearranged so that they are aligned on both sides of the injection passage14, and they can assume, as desired, a closed position in which they arein contact, and an open position in which they are separated from eachother, where the slides close the radial recesses of the nozzlereceptacle regardless of their position.

[0084] Moreover, the nozzle receptacle 1 is penetrated by an air conduit13 which opens between these slides 11, 12 and which is connected to apressurized air source Sa, where the slides can thus close the airconduit 13 in their closed position and open it in their open position.

[0085] The movement of the internal part 34 of the core 3, which allowsthe later to change from its support position to its open position andvice versa, is controlled by a double-acting hydraulic cylinder 5, whichis arranged in the vicinity of the second side E2 of the mold and whichcan displace the second base 32 of the core 3.

[0086] To obtain the centering support of the core 3 on the nozzlereceptacle 1, the hydraulic cylinder 5 displaces the second base 32 ofthe core, in the direction X2, to a stop B that defines a length L34 ofthe internal part 34 of the core 3 for which this internal part 34undergoes, due to the application of its tip 343 against the nozzlereceptacle 1, an elastic compression which determines the support forceF2 mentioned above.

[0087] As shown in the left part of FIG. 2, it is possible to impart tothis compression a predetermined and fixed value, to limit the course ofthe piston 51 of the hydraulic cylinder 5 by proceeding in such a mannerthat, for example, this piston abuts against a stop B on an edge of theplate P6 and/or the base 32 abuts a stop B on an internal flange of theplate P6.

[0088] After the injection of the skirt J and optionally of the neck Cof the tube T, the hydraulic cylinder is controlled to release thesecond base 32 of the core along the direction of injection X1, thusmaking it possible to separate the tip 343 of the internal part 34 ofthe core from the nozzle receptacle 1, and thus allowing the injectionof the cup which closes the spout D (FIG. 3).

[0089] The plates of the mold are perforated in a known manner bychannels which notably allow removal of the heat contributed by theinjected molten material, and the solidification of the tubes aftertheir injection.

[0090] Nevertheless, the preferred application of the mold of theinvention for the injection molding of flexible tubes, including tubeshaving a relatively small size, requires finding specific solutions.

[0091] For this purpose, it is first useful to proceed in a maimer suchthat the molding tools 1, 2, and 3, at least when the axial force F1+F2is applied, are arranged, one with respect to each other andtransversely with respect to the injection direction X1, with a firstpredetermined maximum clearance Jm1 (not shown) and to proceed in such amanner that they are arranged, with respect to the plates P1-P8, withanother predetermined maximum clearance Jm2 (not shown) that is greaterthan the first maximum clearance Jm1.

[0092] Moreover, the plates P1-P8 are regulated, as far as theirtemperature is concerned, so that they present, between themselves, adifferential dilatation which is less than the second maximum clearanceJm2.

[0093] Thanks to these measures, the molding tools 1, 2 and 3 assume,each with respect to the others, a relative position during theinjection which is substantially independent of the dilatation of thestacks of plates P1-P8.

[0094] To obtain an optimal operation of the mold of the invention, itis also useful to provide specific means which allow the establishment,along the molding pin 36, of temperature gradient adequate to allow theflow of the injection material.

[0095] For this purpose, the internal part 34 of the core is traversedby an axial channel 340, in which is housed a hollow needle 35 allowingthe circulation of cooling fluid, for example water.

[0096] The hollow needle 35 comprises a distribution end 354 arranged,in the axial channel 340, in proximity to the tip 343 of this internalpart 34, and a connection end 353 arranged in the second base 32 of thecore, and connected, when the mold is used, to a source Sf of coolingfluid, such as a pressurized water pipe.

[0097] Moreover, the needle 35 and the axial channel 340 are separatedfrom each other by an interstice 355, which offers a circulation routeto the fluid injected into the needle 35 allowing it to return towardthe second base 32 of the core.

[0098] Moreover, the internal part 34 and the external part 33 of thecore 3 both have axial cross sections which work in mutual cooperationto ensure a diffusion of heat that varies along the molding pin 36.

[0099] More precisely, the internal part 34 has a first axial section341 and a second axial section 342 which succeeds the first in thedirection of the tip 343 of this internal part.

[0100] Similarly, the external part 33 has first and second axialsections, 331 and 332, both being arranged approximately opposite thefirst and second axial sections, 341 and 342, of the internal part 34.

[0101] The first axial sections 331 and 341 are radially spaced by arelatively large interval, so that they ensure a thermal coupling whichdetermines a relatively weak thermal flow for a predeterminedtemperature difference between the axial channel 340 and the externalsurface of the molding pin 36.

[0102] By contrast, the second axial sections 332 and 342 are not spacedradially from each other except by a very small clearance, so that theyensure a thermal coupling which determines a relatively large thermalflow for a predetermined temperature difference between the axialchannel 340 and the external surface of the molding pin 36.

[0103] By means of this structure, the heat contributed by the moltenmaterial is primarily discharged in the vicinity of the tip 343 of theinternal part of the core 3, and in a much more moderate manner at adistance from this tip 343, so that the temperature at a distance fromthis tip is maintained at a value sufficient to ensure a satisfactoryflow of the molten material intended to form the skirt J of the tube.

[0104] As shown in FIGS. 8 and 10, the injection passage 14 comprises acentral feed channel 40 and radial feed channels, such as 44-46, each ofwhich is hollowed out in the internal part of the core and extends fromthe central channel 40 to a corresponding zone, labeled Zd1, Zd2 andZd3, of connection with the spout D.

[0105] It is appropriate to note that Dp denotes the perimeter of thespout D, that is the perimeter of the visible circle in FIG. 8, and thatLr1, Lr2 and Lr3 denote the respective widths of the radial channels 44,45 and 46 at the place where they are connected to the spout D; it isadvantageous to proceed in such a manner that the cumulative connectionwidths Lr1, Lr2, Lr3 of the radial feed channels 44-46 represent atleast 15% of the perimeter Dp of the spout D, and even moreadvantageously 25% of this perimeter, so as to ensure a maximumspreading of the sheets of molten material which traverse these radialchannels and to ensure as quickly as possible a constitution of anannular flow of the material at the outlet of the zones Zd1, Zd2, Zd3.

[0106] To preserve as large as possible a support surface on the nozzlereceptacle for the end 361 of the core, it is particularly advantageousfor the radial channels 44-46 to have a width which increases, along acentrifugal radial direction, until it reaches a maximum width Lr1, Lr2,Lr3 in the zone Zd1, Zd2, Zd3 of connection to the spout D.

[0107] Moreover, as shown in FIG. 9, the molding cavity K has an annularnarrowed zone Ze beyond the zone Zd1, Zd2, Zd3 of connection of eachradial channel 44-46 to the spout D; the presence of such a narrowedzone Ze also promotes spreading of the sheets of molten material.

[0108] As shown in FIG. 1, each one of the slides 11 and 12 is connectedat a distance from the injection passage 14 to an inclined surface S1 ofthe first block E10 of the plates, and this first inclined surface S1works in cooperation with a second inclined surface S2 of the secondblock E20 of plates to guarantee a fixed radial position of this slide11, 12 in the closed position of the mold.

[0109] As is also shown in FIG. 10, the nozzle 4 has a stop plug 43 atits outlet 42 which is controlled, in its translational movement, tointerrupt the flow of injection material at the site of the centralinjection channel 40 at the end of the injection.

[0110] The mold of the invention, in particular in the case where thejoint plane PJ passes between the nozzle receptacle 1 and the impression2, makes it possible to proceed in such a manner that the internalsurface and the external surface Ji and Je of the skirt J of the tubeform between themselves, in a mid-plane M of the tube, that is in theplane of FIG. 3, an angle of less than 0.002 radians.

[0111] The invention also concerns a method for the manufacture of tubeswhose specificity resides notably in the manner of using the mold asdescribed above.

[0112] This method substantially comprises a molding phase and a moldremoval phase, the molding phase consisting in forming the tube byinjecting into the molding cavity K, through the central injectionchannel 40, a molten thermoplastic injection material along anorientation such that the spout D is molded in a part of the moldingcavity K that is adjacent to the central injection channel 40.

[0113] The phase of mold removal, which succeeds the molding phase, andwhich occurs after solidification of the injected material,substantially comprises a holding operation, a mold release operation,an opening operation, and an ejection operation.

[0114] The holding operation consists in temporarily holding the tube Tin place, notably by means of slides 11 and 12, until this tube isejected from the molding cavity K by the ejection operation.

[0115] The mold release operation consists in partially extracting thecore 3 from the tube T, so that this tube can then slide easily withrespect to the core.

[0116] According to the invention, the opening operation is consecutiveto the mold release operation and it consists in opening the moldingcavity at the mold joint PJ between the neck C and skirt J of the tube.

[0117] Moreover, the holding operation, which is carried out by holdingthe tube T by the spout D by means of slides 11 and 12 that have beenplaced beforehand in a mutually close position before the moldingoperation, is continued during the opening operation.

[0118] Moreover, the method of the invention preferably comprises anaccompanying operation, which is concomitant with at least one of theoperations of mold release and of opening, and which consists in blowingair between the core 3 and the tube T.

[0119] The ejection operation then essentially consists in interruptingthe holding operation by separating the slides 11 and 12 from eachother, and in blowing air between the separated slides and the externalsurface De of the spout D.

[0120] Finally, the holding operation is advantageously interruptedbefore the end of the opening operation.

[0121] Thus, the sequence of operations is preferably as follows.

[0122] First, the molten material is injected into the molding cavity Kat a high pressure, preferably 1250-2500 bar, while the compressionforce F1 is applied to the stack formed by the plates P1-P8 to hold themin close contact with each other, the slides 11 and 12 are closed, andthe hydraulic cylinder 5 pushes the support surface 302 of the internalpart 34 of the core 3 against the support surface 102 of the nozzlereceptacle 1.

[0123] Toward the end of the injection, the hydraulic cylinder 5 iscontrolled to release the internal part 34 of the core 3 to allow theinjection material to form the cup which closes the spout D. Then, thestop plug 43 is actuated to stop the flow of the molten material towardsthe molding cavity K.

[0124] After solidification of the injected material the compressionforce F1 ceases to be applied, and the plates P4 and P5 are slightlyseparated from each other while air is blown between the core 3 and thetube T. The relative movement of the plates P4 and P5 then allows themold release collar 39 to detach the base of the skirt J of the tubefrom the molding pin 36, this detachment propagating along the entirelength of the skirt J due to the double effect of the movement of theplates P4 and P5 and of the pressure of the blown air.

[0125] The mold is then opened at the mold joint PJ, that is by relativeseparation of the plates P3 and P4.

[0126] Even before the movement of opening the mold at the mold joint iscompletely finished the slides 11 and 12 are separated from each otherwhile the air is blown through the air conduit 13.

[0127] The tube T formed then falls by its own weight between the twoparts formed by the mold which is open at the mold joint.

[0128] As will be understood by a person skilled in the art upon readingthe preceding description, the fact of providing the mold joint PJbetween the nozzle receptacle and the impression offers, by comparisonto the solution which consists in providing it at the base of the skirtJ of the tube, the advantage that the tube T can then be ejected fromthe mold after the latter has been opened over a length barely greaterthan the length of the tube, while a mold which has a mold joint at thebase of the tube must be opened over a length approximately twice aslong to first allow the core to become disengaged from the impression,and then to allow the tube to become disengaged from the core.

[0129] Moreover, although the preceding description illustrated only onemolding cavity K in the set of plates P1-P8, a person skilled in the artwill understand that several molding cavities, for example 8, 16, 32 ormore, can be provided in the same set of plates.

[0130] Similarly, a person skilled in the art will understand that theword conical, as applied here to the centering surfaces 101, 102, 201,202, 301 and 302, has a broad meaning which includes any surface shapewhich is functionally equivalent to a conical surface from the point ofview of the centering which it allows.

[0131] Indeed, although a conical surface in the strictest geometricsense constitutes a centering surface which is both effective and easyto construct, a pyramidal surface, for example, is included in the classof the conical surfaces, in the meaning which is given here to the wordconical.

1. Mold for injection molding of a tube (T) having a distribution spout(D) surmounting a neck (C) that tapers radially to a tubular skirt (J)and is made of a thermoplastic injection material which is flexible atroom temperature, this mold comprising plates (P1-P8) which are appliedto each other to form a stack (E10, E20) extending along an injectiondirection (X1) which is transverse with respect to the plates (P1-P8),from a first side (E1) where a hot block (Q) containing the molteninjection material is located, to a second side (E2) which is at adistance from the first one (E1), and a set of molding tools comprisingat least one nozzle receptacle (1), an impression (2) and a core (3)housed in the stack of plates, the nozzle receptacle (1) being adjacentto the hot block (Q) and receiving a nozzle (4), which has an inlet (41)which communicates with the hot block (Q) and an outlet (42) whichcommunicates, through an injection passage (14), with a molding cavity(K), the core (3) comprising at least a first base (31) that isextended, along a direction (X2) which is the reverse of the injectiondirection (X1) by a molding pin (36) housed in the impression (2) andending in a free end (361), the molding cavity (K) being delimited atleast by the nozzle receptacle (1), the impression (2) and the moldingpin (36) of the core and extending along the injection direction (X1)from the injection passage (14), the core (3) being held in the stack ofplates by at least its base (31) and by the free end (361) of themolding pin (36) and the stack of plates comprising two blocks (E10,E20), which are selectively applied against each other at an interfacebetween two adjacent plates forming a mold joint (PJ) which allowsopening or closing the mold, as desired, characterized in that themolding tools of the assembly, comprising at least the nozzle receptacle(1), the impression (2), and the core (3), present respective pairs ofat least partially conical surfaces (101, 102, 201, 202, 301, 302) whichare oriented along the injection direction (X1), in that these moldingtools (1, 2, 3) are mutually centered and aligned with one another, bypairs of tools constituted next to each other (1-2, 2-3, 3-1), by meansof an axial force (F1+F2) that moves the respective support surfaces(101, 201; 202, 301; 302, 102) of the tools of each constituted pair(1-2, 2-3, 3-1) toward one another, and in that each support surface(101, 201, 202, 301, 302, 102) of each tool (1, 2, 3) of eachconstituted pair (1-2, 2-3, 3-1) is formed by a part of this tool thatis deprived of functional mobility transverse to the injection direction(X1).
 2. Mold according to claim 1, characterized in that these supportsurfaces (101, 102; 201, 202; 301, 302) form, by two-by-two contact, atleast three interfaces (101-201, 202-301, 302-102) through which themolding tools (1, 2, 3) bear against each other, two-by-two, incentering fashion, and in that the support surfaces (101, 102; 201, 202;301, 302) presented by the molding tools to each one of these threeinterfaces (101-201, 202-301, 302-102) are constituted by respectivesingle-block parts of these molding tools (1, 2, 3).
 3. Mold accordingto any one of the preceding claims, characterized in that the nozzlereceptacle (1) and the impression (2) are each formed of a single piece.4. Mold according to any one of the preceding claims, characterized inthat the mold joint (PJ) passes between the nozzle receptacle (1) andthe impression (2).
 5. Mold according to any one of the precedingclaims, characterized in that the molding pin (36) has a surfacecondition which, in order to obtain minimal adhesion of the tube (T) tothis molding pin (36) after injection, is at least equivalent to asurface condition obtained by the application of at least one of thesurface treatments consisting of sandblasting, a micro-finishingtreatment, laser treatment, and chemical treatment.
 6. Mold according toany one of the preceding claims, characterized in that the pair ofsupport surfaces (302, 102) which the core (3) and the nozzle receptacle(1) present consists of a concave support surface (302) of the core (3)and a convex support surface (102) of the nozzle receptacle (1) whichresults in the distribution spout (D) of the tube terminating in a cup.7. Mold according to any one of the preceding claims, characterized inthat the nozzle receptacle (1) is shaped to mold at least an externalsurface (Ce) of the neck (C) of the tube, to a zone of connection (Zc)with skirt (J).
 8. Mold according to any one of the preceding claims,characterized in that the molding pin (36) of the core extends from thefirst base (31), molds an internal surface (Ji) of the skirt (J) andpresents a shoulder (362) bordering its free end and capable of moldingan internal surface (Ci) of the next (C).
 9. Mold according to claim 8,characterized in that the core (3) comprises an external part (33) andinternal part (34), in that the internal part (34) extends, along adirection (X2) which is the reverse of the injection direction (X1),from a second base (32) of the core (3) to a point (343) disposed at thefree end (361) of the molding pin (36), and in that the internal part(34) is mounted so that it axially slides in the interior of theexternal part (33) between a support position, in which the tip (343)rests against the nozzle receptacle (1), and a release position, inwhich the tip (343) is at a distance from the nozzle receptacle (1). 10.Mold according to claim 9, characterized in that the tip (343) of theinternal part (34) of the core molds an internal surface (Di) of thespout (D).
 11. Mold according to any one of the preceding claims,characterized in that slides (11, 12) are mounted so they can undergotranslational movement in radial housings (110, 120) of the nozzlereceptacle (1) to mold an external surface (De) of the spout (D). 12.Mold according to claim 11, characterized in that the slides (11, 12),in the open position and in the closed position, seal tightly thehousings (110, 120) of the nozzle receptacle (1) in which they aremounted so they can move.
 13. Mold according to claim 12, characterizedin that the slides (11, 12) are two in number, they are arranged so theyare aligned with one another on both sides of the injection passage(14), and they are mounted so they can be moved, transversely withrespect to the injection direction (X1), between a closed position wherethey are in contact and an open position where they are mutuallyseparated, in that the nozzle receptacle (1) is penetrated by an airpipe (13) that opens between the slides (11, 12) and that is connectedto a pressurized air source (Sa), and in that the slides close and openthe air pipe (13) in their closed position and in their open position,respectively.
 14. Mold according to any one of the preceding claims,combined with claim 9, characterized in that it comprises, from thesecond side (E2) a hydraulic cylinder (5) which selectively displacesthe second base (32) of the core, and in that, to obtain the centeringsupport of the core (3) on the nozzle receptacle (1), the hydrauliccylinder (5) displaces the second base (32) of the core, along thedirection (X2) which is the reverse of the injection direction (X1), toa stop (B) which defines a length (L34) of the internal part (34) of thecore (3) for which this internal part (34) of the core undergoes anelastic compression that is predetermined by support of its tip (343)against the nozzle receptacle (1).
 15. Mold according to claim 14,characterized in that the hydraulic cylinder (5) is a double-actinghydraulic cylinder capable of selectively releasing the second base (32)of the core along the injection direction (X1) after injection of theskirt of the tube, thus making it possible to separate the tip (343) andthe nozzle receptacle (1) from each other.
 16. Mold according to any oneof the preceding claims, combined with claim 10, characterized in thatthe internal part (34) of the core is traversed by an axial channel(340) in which a hollow needle is housed (35), extending from aconnection end (353) arranged in the second base (32) of the core to adistribution end (354) arranged in proximity of the tip (343) of thisinternal part (34), the connection end (353) of this needle (35) beingconnected, during operation of the mold, to a source (Sf) of coolingfluid, and the needle (35) and the axial channel (340) being separatedfrom each other by interstice (355) which presents to the fluid injectedinto the needle (35) a circulation path which returns toward the secondbase (32) of the core.
 17. Mold according to any one of the precedingclaims, combined with claims 9 and 10, characterized in that theinternal part (34) and the external part (33) of the core both presentfirst and second axial sections (331, 332; 341; 342), where the secondones (332, 342) are relatively closer to the tip (343) than the firstones (331, 341), in that the first axial sections (331, 341) achieve,between the internal and external parts (34, 33) of the core, a thermalcoupling which determines a first thermal flow, in that the second axialsections (332, 342) achieve, between the internal and external parts(34, 33) of the core, a thermal coupling which determines a secondthermal flow, and in that the second flow is greater than the firstflow.
 18. Mold according to any one of the preceding claims,characterized in that the molding tools (1, 2, 3) are arranged, one withrespect to the other, so that there is a maximum clearance (Jm1), inthat the molding tools (1, 2, 3) are arranged, with respect to theplates (P1-P8), with a second maximum clearance (Jm2) that is greaterthan the first maximum clearance, and in that the plates (P1-P8) areregulated as far as their temperature is concerned so as to present,between themselves, a differential dilatation which is less than thesecond maximum clearance (Jm2).
 19. Mold according to any one of thepreceding claims, characterized in that the injection passage (14)comprises a central feed channel (40) and radial feed channels (44-46),each of which extends from the central channel (40) to a connection zone(Zd1, Zd2, Zd3) with a spout (D), where this radial channel (44-46) hasa connection width (Lr1, Lr2, Lr3) or where the spout (D) has apredetermined perimeter (Dp), and in that the cumulative connectionwidths (Lr1, Lr2, Lr3) of the radial feed channels (44-46) represent atleast 15% of the predetermined perimeter (Dp) of the spout (D).
 20. Moldaccording to claim 19, characterized in that the cumulative connectionwidths (Lr1, Lr2, Lr3) of the radial feed channels (44-46) representmore than 25% of the predetermined perimeter (Dp) of the spout (D). 21.Mold according to any one of claims 19 and 20, characterized in that theradial channels (44-46) have a width that increases along a centrifugalradial direction until it reaches a maximum width (Lr1, Lr2, Lr3) in thezone of connection (Zd1, Zd2, Zd3) with the spout (D).
 22. Moldaccording to any one of claims 19-21, combined with claim 9,characterized in that the molding cavity (K) has an annular narrowedzone (Ze) beyond the zone of connection (Zd1, Zd2, Zd3) of each radialchannel (44-46) with the spout (D).
 23. Mold according to any one of thepreceding claims, combined with claim 11, characterized in that eachslide (11, 12), at a distance from the injection passage (14), isconnected to an inclined surface (S1) of the first block (E10) of platesthat works in cooperation with an inclined surface (S2) of the secondblock (E20) of plates to guarantee a fixed radial position for the slide(11, 12) in the closed position of the mold.
 24. Mold according to anyone of the preceding claims, characterized in that the nozzle (4)comprises a stop plug (43) that makes it possible to interrupt the flowof injection material from the hot block (Q) toward the tube (T) at theheight of the central injection channel (40).
 25. Mold according to anyone of the preceding claims, characterized in that the internal surfaceand the external surface (Ji, Te) of the skirt (T) form betweenthemselves, in a mid-plane (M) of the tube, an angle of less than 0.002radians.
 26. Method for the manufacture of a tube (T) having adistribution spout (D) surmounting a neck (C) that radially tapers to aflexible tubular skirt (J), this method substantially comprising amolding phase and a mold removal phase; the molding phase, consisting informing the tube by injecting a molten thermoplastic injection materialthrough a central injection channel (40) into a molding cavity (K) thathas a mold joint (PJ) and that is at least partially delimited by a core(3) and an impression (2), the spout (D) being molded in a part of themolding cavity (K) adjacent to the injection passage (14); and the moldremoval phase, which succeeds the molding phase after solidification ofthe injection material, comprising a holding operation which consists intemporarily holding the tube (T), a mold release operation whichconsists in partially extracting the core (3) from the tube, an openingoperation which consists in opening the molding cavity (K), and anejection operation which consists in ejecting the tube (T) from themolding cavity (K), the opening operation being consecutive to the moldrelease operation and consisting of opening the molding cavity at themold joint (PJ) between the neck (C) and the skirt (J) of the tube,characterized in that it comprises an accompanying operation concomitantwith at least one of the operations of mold release and of opening, andwhich consists in blowing air between the core and the tube. 27.Manufacturing method according to claim 26, characterized in that theholding operation is carried out by holding the tube (T) by the spout(D) by means of slides (11, 12) which were placed beforehand in amutually close position before the molding operation, and in that thisholding operation continues during the opening operation. 28.Manufacturing method according to claim 27, characterized in that theejection operation consists in interrupting the holding operation byseparating the slides (11, 12) from each other, and in blowing airbetween the separated slides and an external surface (De) of the spout(D).
 29. Manufacturing method according to any one of claims 26-28,characterized in that the holding operation is interrupted before theend of the opening operation.